configure: Add -D__USE_MINGW_ANSI_STDIO=1 to CPPFLAGS on MinGW64

This enables a more POSIX-compliant printf implementation, that
allows using length modifiers like 'z'.

configure

@@ -3415,7 +3415,7 @@ probe_libc(){
     # MinGW64 is backwards compatible with MinGW32, so check for it first.
     elif check_${pfx}cpp_condition _mingw.h "defined __MINGW64_VERSION_MAJOR"; then
         eval ${pfx}libc_type=mingw64
-        add_${pfx}cppflags -U__STRICT_ANSI__
+        add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
     elif check_${pfx}cpp_condition _mingw.h "defined __MINGW32_VERSION"; then
         eval ${pfx}libc_type=mingw32
         check_${pfx}cpp_condition _mingw.h "__MINGW32_MAJOR_VERSION > 3 || \